Blood analyzers are known to count the numbers of red blood cells, white blood cells, and platelets. Such blood analyzers measure the red blood cells and platelets from a blood sample of diluted blood, and measure the white blood cells from samples of hemolyzed blood. Electrical resistance methods for detecting the electrical resistance of the sample, and flow cytometric methods for detecting the scattered light from a sample irradiated with light are used in these measurements. The electrical resistance signals employed in the measurements using the electrical resistance method and scattered light signals employed in the measurements using flow cytometry reflect the size of the blood cell, and red blood cells, white blood cells, and platelets can be counted using the signals.
Many such blood analyzers have the function of classifying white blood cells. White blood cell classification classifies white blood cells as lymphocytes, monocytes, neutrophils, eosinophils, and basophils. These types of white blood cells can not be classified simply by information on the size of the blood cell since there are very similar in size. In this case, white blood cells are classified by distributing blood in a plurality of aliquots, preparing a plurality of measurement samples by mixing different types of reagents in the respective aliquots, then measuring the plurality of measurement samples by various methods.
For example, the model SF-3000 manufactured by Sysmex corporation is configured to prepare a first measuring sample by admixing a reagent for four classifications of white blood cells in a first blood (aliquot), to irradiate the first measuring sample with light, to detect the low angle scattered light and high angle scattered light, and to classify white blood cells in four classifications of lymphocytes, monocytes, eosinophils, and a group comprised of neutrophils and basophils based on the low angle scattered light signals and high angle scattered light signals. On the other hand, SF-3000 is configured to prepare a second measuring sample by admixing a reagent for classifying basophils in a second blood (aliquot), to irradiate the second measuring sample with light, to detect the low angle scattered light and high angle scattered light, and to classify white blood cells in two classifications of basophils and other (lymphocytes, monocytes, neutrophils, and eosinophils) based on the low angle scattered light signals and high angle scattered light signals. And SF-3000 is capable of classifying white blood cells in five classifications from both classification results (refer to U.S. Pat. No. 5,677,183).
Similarly, dividing blood into two aliquots and preparing two types of measuring samples by mixing reagents with the respective aliquots, then measuring these aliquots and classifying the white blood cells in five categories is widely performed. For example, the models XE-2100i and XT-2000i manufactured by Sysmex Corporation are configured to prepare a first measuring sample by admixing a reagent for four classifications of white blood cells in a first blood, to irradiate the first measuring sample with light, to detect the side scattered light and fluorescent light, and to classify white blood cells in four classifications of lymphocytes, monocytes, eosinophils, and a group comprised of neutrophils and basophils based on the side scattered light signals and fluorescent light signals. On the other hand, XE-2100i and XT-2000i are configured to prepare a second measuring sample by admixing a reagent for basophil classification in a second blood, to irradiate the second measuring sample with light, to detect the forward scattered light and side scattered light, and to classify the white blood cells as basophils and other based on the forward scattered light signals and side scattered light signals.
Furthermore, the ADVIA manufactured by Bayer Corporation prepares a first measuring sample by admixing a reagent for four classifications of white blood cells in a first blood, irradiates the first measuring sample with light, detects the scattered light and absorbed light, then classifies the white blood cells in four classifications of lymphocytes, monocytes, eosinophils, and a group comprised of neutrophils and basophils based on the scattered light signals and absorbed light signals. The other hand, ADVIA prepares a second measuring sample by admixing a reagent for basophil classification in a second blood, irradiates the second measuring sample with light, detects the low angle scattered light and high angle scattered light, and classifies the white blood cells as basophils and other based on the low angle scattered light signals and high angle scattered light signals.
Still further, the Pentra manufactured by ABX Corporation prepares a first measuring sample by admixing a reagent for four classifications of white blood cells in a first blood, irradiates the first measuring sample with light, detects the absorbed light, detects the electrical resistance (impedance) in the first measuring sample, classifies the white blood cells in four classifications of lymphocytes, monocytes, eosinophils, and a group comprised of neutrophils and basophils based on the electrical resistance signals and absorbed light signals. The other hand, Pentra prepares a second measuring sample by admixing a basophil classification reagent in a second blood, detects the electrical resistance of the second measuring sample, and classifies as the basophils and other based on the electrical resistance signals.
Still further, apparatuses are provided that classify white blood cells from a single blood sample (aliquot). These apparatuses are configured to classify five types of white blood cells using three or more detection signals (for example, refer to U.S. Pat. No. 5,138,181). For example, the LH series of apparatuses manufactured by Beckman-Coulter Corporation prepare a single measuring sample by admixing a white blood cell classification reagent in a blood sample, irradiate the measuring sample with light, and detect the forward scattered light, as well as detect the direct current electrical resistance and high frequency electrical resistance in the measuring sample, and classify the white blood cells into five categories based on the three detection signals of the direct current electrical resistance signals, high frequency electrical resistance signals, and forward scattered light signals (refer to WO88/007187). Moreover, the Celldyn series of apparatuses manufactured by Abbott Laboratories prepares a single measuring sample by admixing a white blood cell classification reagent in a blood sample, irradiate the measuring sample with light, detect the scattered light at 0 degrees, scattered light at 10 degrees, 90 degree polarized scattered light, and 90 degree depolarized scattered light, and classifies white blood cells in five categories based on the 0 degree scattered light signals, 10 degree scattered light signals, 90 degree polarized scattered light signals, and 90 degree depolarized scattered light signals (refer to WO93/016384).
As described above, in conventional blood analyzers, a plurality of aliquots are required to classify white blood cells in five classifications, or three or more signals are required to classify white blood cells in five classifications by using a single aliquot. More blood is necessary when a plurality of aliquots are required than using a single aliquot, and a plurality of mixing chambers are required to prepare measuring samples from the respective aliquots. When three or more signals are needed, the structure of the apparatus becomes complex since many photoreceptor elements and electrical resistance detecting elements are required to detect the respective signals.
Furthermore, flow cytometers installed in such blood analyzers are provided with a flow cell through which the liquid of the sample flows, light source for irradiating the flow cell with light, and photoreceptor elements, such that the light from the light source is scattered by the particles (blood cells) in the flow cell, and fluorescent light is generated by particles stained with fluorescent dye that receive the irradiating light, the scattered light and fluorescent light is received by the photoreceptor elements, and the received light signals are analyzed in the process of analyzing the sample. Although photodiodes, photomultipliers and the like may be used as the photoreceptor elements, high sensitivity photomultipliers are generally used as the fluorescent photoreceptors due to the weakness of the fluorescent light compared to the scattered light. Further, a flow cytometer has been disclosed that uses avalanche photodiode (APD) as a fluorescent light photoreceptor as an alternative to the photomultiplier (refer to WO94/29695).
Since the avalanche photodiode has different sensitivity characteristics than other photoreceptors, such as typical photodiodes, photomultipliers and the like, adequate performance cannot be achieved by simply replacing other photoreceptors with the avalanche photodiode directly.